An apparatus of the generic type is also disclosed, for example, in DE 199 49 005, DE 198 58 428, DE 101 06 699 or DE 10 2004 023 739. All the here cited documents of the state of the art disclose a coordinate measuring machine for measuring structures on a substrate. Herein the substrate is placed on a stage moveable in the X coordinate direction and Y coordinate direction. The coordinate measuring machine is formed such that the positions of structures or edges of structures can be determined by a measuring lens. Herein the position of the measuring stage is determined by an interferometer. It is, however, possible to determine the position of the stage in other ways, wherein ultimately the position of the edge in relation to a coordinate system of a measuring machine is determined.
A coordinate measuring machine as used for measuring structures on wafers and masks used for their manufacture has been disclosed in the paper entitled “Pattern Placement Metrology for Mask Making” by Dr. Carola Blasing. The paper was held at the Semicon Education Program Convention in Geneva on Mar. 31, 1998. The description given there is the basis for a coordinate measuring machine, of which various models are already commercially available.
U.S. Pat. No. 5,136,149 discloses a focusing method for an optical head. In the focusing process the object is obliquely illuminated. The light returned from the object is directed onto a Position Sensitive Device (PSD). The focus position and the tilt of the object in space can be determined from the PSD signal. The apparatus proposed here is not a coordinate measuring machine.
U.S. Pat. No. 6,677,565 discloses a method for high-speed autofocus. Herein a light pattern is projected onto the surface of an object to be measured. Analysis of the image of the light pattern returned by the object is used to determine the focus position and the tilt of the object. This document does not deal with the problems arising from the measurement of positions of structures on a substrate (mask).
U.S. Pat. No. 6,924,929 discloses a microscope, comprising a stage translatable in a horizontal direction. A line sensor is used to record an image of the sample during movement of the stage. The microscope proposed here does not make reference to the measurement of positions of structures on a substrate.
German Patent Application Publication DE 199 63 345 A1 discloses an optical measuring arrangement and a method for inclination measurement. This document likewise does not deal with the measurement of positions of structures on a substrate.
U.S. Pat. No. 6,259,960 discloses a system for the inspection of defects on a substrate (wafer). An image of a defect is generated by an electron microscope. Information about the size and position of a defect on a wafer, for example, can be called up from a database. An optical measurement of positions of edges of structures is not dealt with in this document. Further an inspection of defects is disclosed, which differs distinctly from a method for measuring positions of structures on a substrate (mask).